I use my SSD (on my desktop) for my operating system and programs, and I bought one large enough to leave room for adding more programs. All of my data are on the traditional moving HDs. Given the cost coming down on SSDs, I can see the temptation to use them for data, but I'd look into the prospects of disk cleanup - you're not supposed to defragment SSDs. At least, last time I checked on it, you weren't supposed to. So what will happen to a drive with data moving around on it a lot?

Defragmenting of harddisks used to be important as is sorted the data blocks of a file so that they were adjacent or near to each other to minimise disk platter and read/write head movements which cost time.

Do a little research on long term use of SSDs. I believe they may have a limited amount of reads and writes (although, obviously, since they are already used on many new laptops this is either a large number or they have overcome previous limitations, but CHECK).

I think whatever allows you to use the laptop at greater speeds should be your C Drive. Audio and Video files will not gain much by higher random access as they do not require much random access (they are large typically contiguous files).